1. Field of the Invention
The present invention relates to an axial-flow fan to be directly driven by a drive shaft of an internal combustion engine, or indirectly driven by means of belt driving, hydraulic driving, motor driving and so on, and, more specifically, to an axial-flow fan in which a fluid flow at a fan blade tip is improved.
2. Description of the Related Art
The axial-flow fan of this type includes a boss member to be directly or indirectly driven by the drive shaft of the internal combustion engine, a hydraulic motor, an electric motor and the like, and a fan blade attached on the periphery of the boss member. The fan blade generates a fluid flow when the boss member is rotated. The fan blade is generally curved into a vane-shape for raking out fluid effectively. Therefore, in the case of the axial-flow fan having such a fan blade, there is a problem in that the fluid passed through the fan flows upstream of the fan and lowers the efficiency of the fan. Therefore, in order to prevent such phenomenon that the fluid passed through the fan flows upstream of the fan, there is proposed an axial-flow fan in which a flow at the fan tip is improved (JP-A-4-86399).
This axial-flow fan includes a substantially triangular centrifugal component element extending substantially in parallel with the plane including an axis of the fan formed integrally on the side of the fan blade. With such centrifugal component element, a part of the fluid passed through the fan flows radially, and the radial flow forms a barrier for air, so that the fluid is prevented from flowing around to the front side of the fan.
Therefore, since the axial-flow fan having the centrifugal component element includes the substantially triangular centrifugal component element formed by bending a part or the entire part of the fan blade tip toward upstream, a fluid flow on the rear edge side of the blade tip is improved. However, there remains a problem in that the fluid flow is not improved over the entire range of air quantities. In addition, in recent years, high loadings in the axial-flow fan are increasingly required in association with increase in horsepower of the internal combustion engine, and thus horsepower consumption tends to increase. When the horsepower consumption increases, a load applied on the fan drive inevitably increases correspondingly. As a consequent, a fan of high loadings and of lower horsepower is required.
In view of such circumstances, the invention is intended to improve a fluid flow on the rear edge side of the blade tip without deteriorating the fluid flow on the front edge side of the blade tip, reduce loss of horsepower without causing a large influence on the loadings, and provide an axial-flow fan having a high fan efficiency and a high performance.
The axial-flow fan according to the invention is characterized in that the blade has a warped portion on the side surface of the blade tip on the rear edge side thereof, the warped portion is formed by bending the blade tip toward upstream at angles between 5 to 30 degrees with a smooth filet R along a line connecting a widthwise position along the blade tip at a length between A and 1/5A, where A represents the chord length A, from the rear edge toward the front edge thereof and a radial position of the rear edge of the blade tip at a radial length between 1/2B and 1/10B from the rear edge of the blade tip, where B represents the radial length of the blade.